1. Field of the Invention
The present invention relates to an air-conditioning device, and more specifically to an air-conditioning device which conditions by blowing air streams of different temperatures from a first passage and a second passage.
2. Description of the Related Art
There has heretofore been known technology as disclosed in, for example, Japanese Unexamined Patent Publication (Kokai) No. 191118/1992. This technology is concerned with an air-conditioning device for vehicles in which an evaporator and a heater core are arranged in a duct. This air-conditioning device is provided with a cool air by-pass that guides the cool air that has passed through the evaporator directly to a first passage that blows the cool air to the upper half body of a passenger, in addition to a duct in which the heater core is contained. By controlling the flow rate of the cool air that passes through the cool air by-pass, the temperature of the air blown from the first passage is controlled to be lower than the temperature of the air that is blown from the second passage to the feet of the passenger.
The above technology, however, has the following inconveniences which will now be described by using a time chart of FIG. 13. That is, in the above-mentioned conventional air-conditioning device, when the temperature is first set at 25.degree. C., a feet mode operation condition is established in which no air is blown from the first passage to the upper half body of the passenger but the hot air of 35.degree. C. (desired blow-out temperature) is blown to the feet of the passenger from the second passage. Then, when the setpoint temperature is changed from 25.degree. C. to 23.degree. C. at a time t, the feet mode operation is automatically changed into a bilevel mode operation in which the air is blown from the first passage and the second passage, and the cool air of 25.degree. C. (desired blow-out temperature) is blown to the upper half body of the passenger from the first passage.
During the feet mode operation before being changed, no air flows into the first passage. Therefore, a first temperature sensor provided in the first passage on the side close to the room detects the temperature of the air which is nearly the same as the temperature (e.g., 25.degree. C.) in the room. Immediately after the change to the bilevel mode operation, therefore, the temperature detected by the first temperature sensor is the temperature in the room, i.e., 25.degree. C. due to a delay in the detecting operation of the first temperature sensor. In the feet mode operation, the cool air by-pass remains closed. When the first temperature sensor is detecting the room temperature (e.g., 25.degree. C.) immediately after the change to the high-level mode operation, the control device works to maintain this condition since the temperature 25.degree. C. is the desired blow-out temperature from the first passage. That is, the control device operates with the cool air by-pass maintained closed. Then, the hot air of 35.degree. C. which is the same as that of the second passage is guided to the first passage; i.e., the hot air is blown to the upper half body of the passenger as shown in FIG. 13 and the passenger feels uncomfortable.
Furthermore, when the bilevel mode operation is changed to a face mode in which the cool air is blown to the upper half body of the passenger from the first passage, and is then changed again into the bilevel mode operation in which the hot air is blown to the feet of the passenger from the second passage, the second temperature sensor in the second passage detects the room temperature until the operation is changed into the bilevel mode. When the temperature detected by the second temperature sensor is just the same as the desired blow-out temperature of the second passage or is close to the desired temperature at a moment when the operation is changed into the bilevel mode operation, the cool air is blown from the second passage during the initial period in which the operation is changed into the bilevel mode operation causing the passenger to feel uncomfortable.